Remark 2.1 
A feature of étale actions is that they can be restricted
and then reconstructed from this restriction.
Observe that \(s \cdot x = s \cdot (p(x) \cdot x) = (sp(x)) \cdot x\) 
and that \((sp(x))^{-1}sp(x) = p(x)s^{-1}s \le p(x)\) .
Thus we may restrict the action to those pairs \((s,x)\)  where \(s^{-1}s \le p(x)\) 
and lose nothing.
We shall not use this result below but it explains why this new approach using actions
is equivalent to the one adopted in [1]}
which uses restrictions and corestrictions.

